The genetic complexity of muscle structure and function will be investigated using the free-living nematode Caenorhabditis elegans. Mutants defective for muscle function will be isolated and analyzed genetically, biochemically, and anatomically. Such mutants identify genes required for development of a functional muscle cell. The genes encoding paramyosin and myosin light chain proteins will be investigated directly using recombinant DNA techniques. The molecular interactions responsible for the heterozygous mutant phenotype of dominant mutations affecting a myosin heavy chain gene will be identified. The long range goals are to identify genes and proteins required for muscle function, and to understand how these components function during sarcomere assembly and contraction. Genetic properties of the nematode transposable element Tcl will be investigated. The nucleotide sequences of Tcl insertions and excisions will be determined. The genetic basis for strain-specific and tissue-specific activity of Tcl will be studied. The long range goals are to understand the biological roles for transposable elements, and to use Tcl as an investigative tool to study the differences between basic genetic mechanisms of germ cells and somatic cells. This work contributes to the national health by describing the molecular mechanisms that underlie fundamental cellular and genetic phenomena.